What is dRTA

dRTA is a rare but serious type of kidney disease that can be inherited (primary dRTA) or be caused by another disorder or medication (secondary dRTA). Primary dRTA is also known as Albright acidosis. Renal refers to the kidney, distal tubular refers to a specific part of the kidney and acidosis means there is too much acid build-up in the blood.

The kidneys have many important roles in the body. One of them is to maintain a balance between acid and base (opposite of acid) by, among others, removing and filtering acids from the blood and into the urine. dRTA occurs when the kidneys can no longer effectively remove the build-up of circulating acids in the blood. This build-up of acids in the blood causes an imbalance known as “acidosis” or “metabolic acidosis”.

Metabolic acidosis is a serious health problem requiring prompt medical attention. dRTA can also cause failure to thrive, kidney stones, brittle bones, hearing loss, digestive problems, as well as other medical problems. Not all people living with dRTA will experience the same health issues. dRTA is part of a class of disorders known as renal tubular acidosis (or renal tubular disease). There are four (4) types of renal tubular acidosis, with primary type 1 dRTA identified as the most common type.

Causes of dRTA 

Primary dRTA has a genetic (inherited) origin, which means it is passed along from parent(s) to child, autosomally - either dominant or recessive.. 

Secondary (or acquired) dRTA can be caused by another disease, mainly autoimmune disorders such as Sjögren's syndrome, systemic lupus erythematosus (SLE), or rheumatoid arthritis. Secondary dRTA can also be caused by certain medications, such as amphotericin B (an antifungal), lithium (a psychiatric medication), and certain antibiotics (pentamidine). 

Symptoms of dRTA

Primary dRTA can cause a wide range of signs and symptoms. Symptoms can begin in infants or as late as adulthood. Not everyone will experience the same symptoms as they can vary depending on such factors related to the specific gene change, level of acidosis (acid in the blood), age of the individual, and even how advanced the disease is. Secondary dRTA usually occurs later in life.

Severe complications can occur in infants with primary dRTA. Early signs and symptoms in babies include nausea and vomiting, dehydration, extreme tiredness, feeding issues and problems with weight gain (also known as failure to thrive). These are symptoms consistent with metabolic acidosis and it’s important to seek medical attention right away for a baby experiencing these symptoms.

Because calcium can be leached from the bones in people living with dRTA, the disease can lead to mineral imbalances and bone disorders. The imbalance of deficient calcium in bones or excess calcium in the blood and urine can cause a softening and weakening of bones. This can lead to rickets in children. Rickets is a condition in which the bones actually bend as they are too soft and do not harden or calcify as normal. Children may also experience stunting of growth and may not reach their full adult height potential. Osteomalacia (a softening of bones in adults) and osteopenia (weakening and brittle bones in adults) are consequences that can lead to increased risk of fracture. Bone disorders are not as common in the dominant (AD dRTA) pattern of inheritance.

Following the loss of calcium salts from the bones, high levels of calcium in the blood and urine can lead to calcium deposits in the kidneys, a condition known as nephrocalcinosis,  leading to kidney stones formation.

If kidney stones keep coming back after they are removed (termed as recurrent), there is an increased risk of Chronic Kidney Disease (CKD) which can impact the filtering ability of the kidneys. Although considered uncommon, people with dRTA may be at higher risk of developing kidney failure, which would ultimately require dialysis or a kidney transplant.

dRTA can also cause low levels of potassium in the blood— a condition known as hypokalaemia. Potassium is a key electrolyte that supports nerve and muscle health. Hypokalaemia can cause severe muscle weakness, breathing difficulties and abnormal heart rhythm (cardiac arrhythmias). In extreme cases of hypokalaemia, severe cardiac rhythm disturbances, paralysis and even death can occur.

Sensorineural hearing loss is linked to primary dRTA, related to changes in the inner ear. This can lead to difficulty in hearing and deafness in some people, but not all.

Patients living with primary dRTA can also experience serious digestive (or gastrointestinal) disorders. The most commonly reported digestive disorders are anorexia, vomiting, diarrhoea and constipation. These symptoms are usually due to metabolic acidosis, but low potassium can also cause digestive problems.

Diagnosis of dRTA

dRTA is diagnosed by a kidney specialist (or nephrologist) using a combination of tests, including a physical exam looking for signs and symptoms of the disease, along with blood and urine tests. If primary dRTA runs in your family, your nephrologist may take a detailed family history to help identify at-risk family members. Genetic testing may be offered to help confirm the diagnosis.

Your doctor may check for other autoimmune diseases that can cause secondary dRTA, such as Sjögren's syndrome or systemic lupus erythematosus (SLE).

Laboratory tests and urine tests (or urinalysis) are routine tests that analyse your blood and urine. Initial blood work for diagnosing dRTA involves measuring electrolytes within the blood, such as sodium, potassium, and chloride. Tests can also measure the blood pH to see if it is too acidic. Blood levels of potassium and carbon dioxide (types of acid) and bicarbonate (a type of base) are measured to help complete the pieces of the puzzle for your healthcare team to make a diagnosis.

Treatment of dRTA

The main treatment for dRTA involves alkali agents, which are used to reduce acid build-up in the blood. Alkali agents can include sodium bicarbonate, potassium bicarbonate, sodium citrate or potassium citrate or a mixture of these agents.

Potassium bicarbonate or potassium citrate can be used when potassium levels in the blood are low (hypokalaemia), or in some people with high blood and urine levels of calcium (hypercalciuria) or calcium kidney stones. Citrate is converted to bicarbonate in the body and helps to correct the acid build-up in the blood. In addition, citrate helps to prevent calcium deposits in the kidney. Sodium (found in sodium bicarbonate, sodium citrate or other sodium salts) can increase calcium levels in the blood and urine.

These treatments need to be given between 2 and 6 times per day to ensure 24-hour coverage of acidosis.